Could too many Covid vaccines be bad?

Australia has just expanded access to a second COVID booster to everyone 30 years and over, while recommending it only for people 50 and over. That means it’s up to people aged 30-49 years to decide whether they would like a second booster, but they will not be actively encouraged.

The promise of COVID vaccines as a means to completely ending the pandemic was short-lived. Just as vaccines matched to the original strain of the virus were being rolled out in late 2020, multiple new variants of concern emerged, with increasing vaccine breakthrough infections.

Vaccines are not as protective against variants such as Omicron and also wane in protection, which is why we have seen continued waves of infection even in highly vaccinated countries. Two doses do not protect against infection with Omicron, especially if you had the Astra Zeneca shot, so high booster rates are essential.

A health care worker prepares a Pfizer Covid vaccine in the pharmacy of the Heidelberg Repatriation Hospital vaccination hub in Melbourne, Monday, September 13, 2021. Source: AAP
A health care worker prepares a Pfizer Covid vaccine in Melbourne. Source: AAP

The strong messaging we received in 2021 about being “double-jabbed” being the end of the road, left many people unaware a third dose was essential. Compared with a stunning 95% of people 16 years and over having two doses, only 70% have had three doses. Yet even the protection of a third dose wanes, even against severe infection and death. But this can be restored with a fourth dose.

Some countries, such as the United States, have recommended fourth doses to anyone over 50 for some time, while Australia has had restricted access, until now just for people over 65.

Why we need a fourth shot

Australia has essentially used a vaccine-only strategy to control COVID since late 2021. Masks and other measures such as QR codes have been largely abandoned and testing is expensive – many cannot afford a regular supply of rapid antigen tests, and PCR tests can cost an individual more than $100.

Antivirals are only available to restricted groups, unless you can afford $1,200 for a private prescription.

Meanwhile, more than 10,000 people have died in Australia, the majority within the supposedly “mild” Omicron wave in 2022 when we were given the message the pandemic was over.

Many of these deaths and hospitalisations could have been prevented by using extra, layered measures to reduce transmission. The crippling of the health system, disruption of workforce, schools and airports, and the burden of long COVID are other reasons to try our best to reduce case numbers. Repeated reinfections should also be prevented, as they increase the risk of death.

A nurse is seen outside of a hospital in Melbourne, Wednesday, July 6, 2022.
A nurse is seen outside of a hospital in Melbourne as concerns rise over COVID-19 sub-variants. Source: AAP

A fourth dose becomes even more crucial when we have no other plan - no mask mandates, no mandated indoor air quality standards nor universal, affordable access to antivirals. It will save lives and reduce the load on our health system.

The BA.5 Omicron subvariant is now taking over, and has even more “escape” from current vaccines. But a fourth dose will help.

Ideally, we would have vaccines matched for Omicron, but these may not be available in Australia for many months, during which time many more lives will be lost from the BA.4/5 wave. Even the original vaccine will still provide better protection with a fourth dose compared with only three doses.

Could too many vaccines be bad?

Some argue about “original antigenic sin” (or “immune imprinting”) as a problem with repeated doses of COVID vaccines - as in, they think after repeated doses the vaccine’s effectiveness will be reduced.

However, this reflects a misinterpretation of what original antigenic sin means - it means the first time you are exposed to a virus or vaccine, the body remembers that first time when it subsequently encounters something similar. But this immune memory can lead to either a blunted or an enhanced response.

The concept arose around influenza, but even that, which has been studied far more than SARS-CoV-2 (the virus that causes COVID), is not conclusive or necessarily detrimental - and we still recommend repeated flu vaccines every year.

There is no evidence of original antigenic sin being a problem for COVID boosters - studies show significantly better protection from four compared to three doses. In people with weakened immunity, even five doses continued to boost the immune response.

When we have better matched boosters, it is likely they too will be offered, but holding out for these for an unknown period of time will result in preventable deaths and chronic illness.

Boy, 10, becomes one of the first children in Queensland to receive their first vaccine at Kippa Ring Communication Vaccination Clinic, Brisbane, Monday, January 10, 2022. Source: AAP
A 10-year-old boy was one of the first children in Queensland to receive their first vaccine in January. Source: AAP

What about younger adults?

ATAGI did not recommend fourth shots for under-30s reportedly because of the low risk of myocarditis following vaccination in young males - but the risk of myocarditis is far higher after COVID infection than after vaccination, and even if that argument held, what about young women?

Omicron causes excess mortality in all adults, even younger ones, so the benefits of expanding access to a fourth dose to everyone 18 years and over would likely outweigh any potential risks.

Health workers miss out yet again, with no specific allowance for them and many being under the age of 30. This will not help the exodus of burnt-out health workers, many of whom got infected in the line of duty.

Meanwhile, we are bracing for a massive wave of BA.4 and 5, predicted to be as bad as the last peak early in 2022. In the absence of other public health measures such as masks, and if a vaccine-only strategy is continued, expanding fourth dose eligibility is the only way to mitigate the next COVID wave.

Much more could be done to mitigate and prevent COVID, by using a “vaccine-plus” strategy of layered measures.

The author of this article is Professor Raina MacIntyre, NHMRC Principal Research Fellow, Head of the Biosecurity Program at the Kirby Institute, and Professor of Global Biosecurity at UNSW.

This article is republished from The Conversation under a Creative Commons licence. Read Access to a second COVID booster vaccine has been expanded to people 30 years and over in full at The Conversation.

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